Fit And Set Up A Bike’s Front Derailleur
Set the front derailleur so that the outer
plate of the derailleur cage – the metal plates that the chain passes through – is
2mm above the big chain-ring and lock it half-tight. Work the front derailleur manually to check
it won’t touch the chain-rings anywhere in it’s range of movement. In case of inteference
raise the derailleur as little as possible to eliminate the clash. Set the cage plates exactly parallel to the
chain-rings. Tighten the fixing or the clamp bolt to lock
the front derailleur in place. Identify the two screws that limit the movement
of the derailleur. They may be labelled ‘L’ & ‘H’, or Low and High. Set the rear derailleur in the lowest gear,
with the chain on the biggest cog wheel at the back. Set the chain in the lowest gear
at the front – the smallest chain-ring. Unclamp or dismount the cable. Turn the pedals
forward. If the chain rubs on the inner plate of the derailleur cage turn the low limit
screw anti-clockwise to allow the spring to move the cage left until the interference
is gone. Otherwise screw in the low limit screw to move the cage right until the chain
brushes it, then go back a quarter turn to silence the rub. Select the lowest gear in the shifter and
close down any barrel adjusters on the cable run. These may be where the cable exits from
the shifter, at a stop on the frame, or just mounted in-line on the cable. Remount or reclamp
the cable. The cable should be neither lose nor tight but passive between the shifter
and derailleur. If the cable is new pull on any exposed length
of inner cable to compress the ferrules and outer-cable into position. If there is no
exposed length of cable you can do this by pedalling and shifting onto a larger chain-ring.
Unclamp the cable and take up any slack that results from this stress test. Click the shifter while turning the pedals.
Turn the barrel adjusters to tighten the cable until the chain shifts onto the next chain-ring. Pedal and use the shifter for the rear derailleur
to select the highest gear – the smallest cog wheel – on the rear hub. If the bike
has three chain-rings make another shift onto the biggest chain-ring. You may need to tighten
the cable with the barrel adjuster while pedalling to enable the chain to move. If the bike only
has two chain-rings it’s already there. Turn the pedals forward. If the chain rubs
on the outer plate of the derailleur cage turn the high limit screw anti-clockwise to
allow the cable to move the cage right until the interference is gone. Otherwise screw
in the high limit screw to push the cage right until the chain brushes it, then go back a
quarter turn to silence the rub. Work the front derailleur to shift the chain
between the chain-rings. If the chain is slow to up shift onto a bigger ring tighten the
cable. If it is slow to drop onto a smaller chain-ring loosen the cable. Run the chain around the two biggest cog wheels,
the fastest at the front and slowest at the back. Don’t thread it through the derailleurs.
Find the shortest length that would connect and add on 1 inch, one complete inner and
outer link. This is usually the ideal length for modern derailleur systems. Thread the chain through the derailleurs and
round the two smallest cog wheels, the slowest at the front and the fastest at the back.
Offer up the two ends of the chain and match the link that makes the chain short enough
so that the bottom run of chain doesn’t rub on swing arm near the top jockey wheel
on the rear derailleur. To reconnect the chain thread it back onto
the bike and hold it in place with a wire bent into a ‘C’ shape; a dead spoke with
the head cut off is ideal. Realign both ends of the chain in the slot
on the chain tool further from the punch with the holes aligned. The rivet sticking out
should be faced toward the punch. Drive it back through the chain by screwing
in the punch on the chain tool. Check how far to push by comparing the back of the link
with others. The position of the driven pin needs to match the height of the others. When the head of the rivet viewed, from the
back, matches its fellows, retract the screw and remove the chain from the chain tool.
Check the link you’ve just been working on it may be stiff and unable to flex like
the others. If it’s stiff it needs to be spread.